Lens



Search Rm w. SCHADE 'May 16, 1939.

LENS

Filed Nov. 19, 1937 F /00mm.

ATTORNEY;

Patented May 1.6, 1939 UNITED STATES `Search Rom LENS Willy schade,Rochester, NJ., assigner to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey Application November 19, 1937, Serial No.175,474

7 Claims.

This invention relates to lens systems, and particularly to imageforming lens systems such as are used in photography.

More specifically it relates to image forming systems of highmagnication, i. e. systems which are particularly useful when employedto have conjugate images vastly different in size. In photography orcinematography, the image on the lm is usually many times smaller thanthe original subject. In lantern slide or cinematographic projectors,the image on the screen is many times larger than that on the slide orfilm. It is an object of the invention to provide an objectiveparticularly suitable for projection purposes or when reversed, forphotographic purposes. For convenience, I include all such lenses underthe self-explanatory term high magnification image lforming systems.

As a high magnification image forming lens, it is common practice to usea Petzval type of lens consisting of two widely spaced achromats, theAone on the long focu's side usually being a cemented doublet and theone on the short focus side being either a cemented or spaced doublet.

It is an object of the present invention to provide a modified Petzvallens system more highly corrected than hitherto. It is a particularobject of the invention to provide such a modif-led Petzval typelens'having the'known advantages of such systems, namely, goodcorrection of spherical aberration and coma, and also having reducedcurvature of field and astigmatism.

In a concurrently led application, Serial Number 175,473 I describe amodified Petzval lens system in which the rear component, i. e. the oneon the short focus side is modified and which is capable of working atcomparatively high relative apertures. The present invention isconcerned specically with the front component and has as its main objectthe improvement of curvature of eld and other aberrations rather than inincreasing the relative aperture. As I pointed out in this copendngapplication, the two inventions may be combined with certain advantages,although from a commercial point of view the added improvement does notat present seem worth while over either system. alone. On the otherhand,'this slight improvement on the lens 'ng case is one of thedescribed in this cope minor objects of the present invention.

According to the invention, the front component of ya Petzval type lens,that is the component toward the long focus side, is modied to include anegative air lens. The term negative air lens is used by those skilledin the art meniscus element spaced behind a doublet and concave thereto.lThe specic lens shown has'a. meniscus element in marginal contact withthe rear surface of the doublet, which permits convenient assemblyduring manufacture. Described in other words, a front component madeaccording to this invention may comprise a negative element (preferablymeniscus) behind a doublet whose rear surface has a curvature morestrongly positive than that of the front surface of the negativeelement. K

Other objects and advantages of this lens will be apparent from thefollowing description when read in connection with the accompanyingdrawing in which:

Fig. 1 shows a typical Petzval lens. Fig. 2 shows a modled Petzval lensincorporating a preferred embodiment of the present invention. A

The typical Petzval lens shown in Fig. 1 coniprises two widely spacedachromats, the front one being a cemented doublet and the rear one beinga spaced doublet. Many variations of this form have been investigated byworkers inl this field and many variations of the separate componentshave been proposed. For example, the rear component may have additionalelements,may have the order of the elements reversed, and/or may includea cemented surface. Furthermore it has been pointed out that the twocomponents need not be separately achromatic, but may be arranged sothat under-correction in one component is compensated for inthe othercomponent. The present invention is not particularly concerned with thisrear component and any of the variations taught in the prior art canprobably be used therewith. f

Y As shown in Fig. 2, the invention primarily concerns the frontcomponent which comprises an a'chromat (or an approximately achromaticcomponent) including a negative airlens bounded by the refractingsurfaces R3 and R4. In vthe arrangement shown the elements l1 and IlIare in marginal contact. but this feature which is convenienty forassembly purposes is not at all necessary to the broad invention. Thepreferred embodiment shown has the following specifications;

Lens Glass Radii Spacings Millimeur Milummr ND=1.6109 I Iii-+ Iii- 38.5:,-iao

u {ND-1.5750 n.+49s.o :.-ao

sl=2.0 N13-1.5224 m R4H-83.9

r=59.6 i|=3.0 Ril-940.0

S1=27.5 Nui-1.6164 IV 11p-+1343 .a.o v-36.0

R1+35.1 Nsxreios s.4.o V nF4-n.0

R=11s.o

It will be noted in this preferred embodiment that the lens III is madeof glass having an index refraction less than 1.55. This fact and theone that the element DI is meniscus are not absolutely necessary, butthese features assist in reducing the Petzval Sum and hence in givingreduced curvature of eld.

The introduction of this element III greatly improves the astigmatismand curvature of field as compared with the arrangement shown in Fig. 1and also improves the other aberrations slightly which are alreadyhighly corrected in the simple arrangement.

Having thus described the principle of my invention and the details ofthe preferred embodiment of it, I wish to point out that it is not'llimited to this specific structure but is of the scope of the appendedclaims.

I claim:

1. A high magnication image forming objective comprising two achromaticcollective components spaced more than one-quarter of and less thantwice the focal length of the objective, the component on the long focusside consisting of a cemented doublet whose cemented surface is convexto the other component and a negative meniscus lens in marginal contactwith the inner element of the doublet.

2. A high magnication image forming objective comprising two achromaticcollective components spaced more than one-quarter of and less thantwice the focal length of the objective,

the component on the long focus side consisting .of y" 7' a cementeddoublet whose cemented surface has 10 a radius of curvature less thaneither of its outer surfaces and greater than one-quarter of the focallength of the objective and a meniscus element concave to the doubletand between the doublet and the other component.

3. A high magnilication image forming objective comprising twoachromatic collective components spaced more than one-quarter of andless than twice the focal length of the objective, the component on thelong focus side consisting of a negative element spaced behind adoublet.

4. A high magnification image forming objective comprising twoachromatic collective combehind a compound member'forming a negative airlens therewith.

7. An objective of the Petzvai type in which the front component is madeup of a plurality of lens elements, two of which are dispersive andenclose a negative air lens and in which the front one of said twodispersive elements is cemented to the rear of a collective element.

WILLY SCHADE.

